Voltage overload arrester for a high-voltage switching system

ABSTRACT

A voltage overload arrester for a high-voltage switching system of the type including a metallic switching housing containing a gaseous insulating medium, and a metallic overload arrester housing, communicative with the switching housing and containing the same gaseous insulating medium. A plurality of discharge current resistor elements are disposed in a columnar arrangement in the arrester housing for discharging voltage overload current surges, and are constructed of an electrically conductive metallic composition having a zinc oxide base. The resistance elements of the inventive apparatus eliminate the need for spark gaps for discharging the voltage overload current surges.

Unlted States Patent 1 1 1 v 1111 3,881,766 Pratsch 1451 May 6, 1975 [54] VOLTAGE ()VERLOAD ARRESTER FOR A 3,390,239 6/1968 Miller 200/148 B HIGH V()LTAGE SWITCHING SYSTEM 3,777,218 12/1973 Kessler 317/71 X Inventor: Rudolf Pratsch, Berlin, Germany Siemens Aktiengesellschaft, Munich, Germany Filed: Sept. 20, 1973 Appl. No.: 399,351

Assignee:

Foreign Application Priority Data Sept. 28, 1972 Germany 2248117 References Cited UNITED STATES PATENTS 11/1959 Oppel ..200/148B '1/1960 Forwald ..200/148B Primary Examiner-James D. Trammell Attorney, Agent, or Firm-Kenyon & Kenyon Reilly Carr & Chapin 57} ABSTRACT A voltage overload arrester for a high-voltage switching system of the type including a metallic switching housing containing a gaseous insulating medium, and a metallic overload arrester housing, communicative with the switching housing and containing the same 4 Claims, 2 Drawing Figures VOLTAGE OVERLOAD ARRESTER FOR A HIGH-VOLTAGE SWITCHING SYSTEM BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates generally to high-voltage switching systems, and in particular, to an improved voltage overload arrester for such systems for discharging current surges flowing therethrough.

2. Description of the Prior Art High-voltage switching system voltage overload ar-.

resting mechanisms generally comprise a plurality of spark gaps and voltage dependent discharge resistors coupled in series thereto which are disposed in an electrically nonconductive housing. An arc discharge occurs across the spark gap electrodes at a predetermined voltage threshold level to discharge current surges. The voltage dependent discharge resistors limit the system current surges so that the current produced by a voltage overload is dissipated. In order for the overload arrester to operate properly, it is necessary that the areover threshold voltage of the voltage of the spark gaps remain substantially constant, and it has been found that the spark gaps of such an arrester operate most effectively in a gaseous atmosphere consisting of nitrogen.

It is desirable, however, from a design point of view, to reduce the structural dimensions of overvoltage arresting mechanisms and improve their performance. These objectives have been partially achieved by filling the housings of voltage overload arresters with a gaseous insulating medium of high dielectric strength, such as an electronegative gas, for example, sulfur hexafluoride. See, for example, U.S. Pat. No. 2,757,261. The threshold voltage of spark gaps operating in such an electronegative gaseous insulating medium, however, generally does not remain constant. and discharge arcs flowing between the electrodes of the spark gaps in such a medium decompose the electronegative gas and form decomposition products which damage the components of the arrester mechanism. These difficulties have been overcome by arrangements such as that disclosed in U.S. Pat. No. 3,099,770, in which the spark gaps are enclosed in a separate housing within the arrester housing which contains a separate gaseous insulating medium. The separate housing, however, and the attendant gas-impermeable seals which must be provided to prevent intermixture of the electronegative gas with the gas contained in the spark gap housing, entail additional undesirable fabrication expense.

SUMMARY OF THE INVENTION It is therefore an object of the invention to provide an improved overload arrester for a high-voltage switching system which overcomes the abovementioned disadvantages of heretofore known overload arresting systems.

The above object is achieved by a voltage overload arrester for a high-voltage switching system of the type including a metallic switching housing containing a gaseous insulating medium, and a metallic overload arrester housing, communicative with the switching housing and containing the same gaseous insulating medium. The improvement of the invention comprises the provision of discharge current resistors, disposed in the arrester housing in a columnar arrangement, which are constructed of an electrically conductive metallic composition having a zinc oxide base, for discharging current surges flowing through the switching system.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view of a high-voltage switching system including an improved voltage overload arrester constructed according to the invention; and

FIG. 2 is a cross-sectional view of another highvoltage switching system illustrating an additional embodiment of an improved voltage overload arrester constructed according to the invention.

DETAILED DESCRIPTION Referring now to the drawings, in particular FIG. 1, there is shown a high-voltage switching system comprising a pair of bus bars 1 and 2 disposed in housings 3 and 4 and coupled to a pair of disconnect switches 5 and 6 disposed above the bus bars. Housings 3 and 4 are part of a metallic switching system housing 18 which encapsulates the components of the installation and contains a gaseous insulating medium. A current transformer 7, an operational grounding switch 10, and a power circuit breaker II are coupled to disconnect switches 5 and 6. The upper terminal of power circuit breaker 11 is coupled to another operational grounding switch I2, a voltage transformer I3, a terminal conductor I5, and an operational grounding switch 14 for the terminal conductor. Conductor 15 may be coupled to an overhead power line or to an electrical cable. Voltage overload arrester 16 comprises a metallic housing 17 which is communicative with switching housing 18 and contains the same gaseous insulating medium, which is preferably sulfur hexafluoride. Voltage dependent, discharge current electrical resistance means, illustrated in schematic form as a plurality of electrical resistors arranged in columnar fashion in series and disposed axially within housing 17, are coupled to switches 5 and 6 and bus bars 1 and 2. The resistors are constructed of an electrically conductive metallic composition having a zinc oxide base and comprising other metallic oxides in combination therewith. An alloy of metal oxides suitable for constructing the resistors of the voltage overload arrester is disclosed in German Pat. No. 1,765,097. The columnar arrangement of the resistors is the same as silicon carbide resistor arrangements in heretofore known voltage overload arrester systems. Resistors 19 may be disposed in a porcelain or other electrically nonconductive housing. The zinc oxide base material causes the resistors of the arrester to exhibit a pronounced voltage dependency which eliminates the need for arc-discharge of current surges by means of spark gaps. Dissipation of voltage overload current surges in the switching system is thus carried out as a pure electrical conduction process in the discharge resistors, and no arc-over occurs in the arrester. This permits the use of gaseous insulating mediums having a high dielectric strength, such as, for example, sulfur hexafluoride, in the overvoltage arrester housing.

The voltage overload arrester constructed according to the invention has considerably smaller dimensions which is a particularly advantageous feature in switching systems utilizing metallic housings. For example, the elimination of the spark gaps of the arrester permits the arrester to be mounted on the switching system housing in a position which produces optimum effectiveness, such as in the horizontal position illustrated in the drawings adjacent disconnect switch 5. Heretofore it has been impossible due to structural limitations to .couple an arrester to a metallic switching housing at a point which produced an optimum protective effect.

Gas-impermeable and pressure-proof feedthrough couplings between the arrester housing and the switching housing, which are generally utilized in conventional arrester systems to prevent contamination of the gases therein, are not required in the described arrester.

However,if it be required, or desired, to facilitate installation and/or maintenance of the arrester, housing l7 may be provided with a feed-through coupling at the ,base thereof.

The embodiment of the invention illustrated in FIG. 2 is similar in all respects to that of FIG. 1 except that housing 17 and the previously described components of the arrester are disposed in a vertical position adjacent switch 14 and terminal conductor 15. This position is also a desirable location for the arrester since it proflduces an optimum protective effect forthe switching system.

While there have been disclosed herein what are considered to be at present preferred embodiments of the invention, it will be understood by those persons skilled in the art that many changes and modifications may be madethereunto. lt vis therefore intended in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the inveiition.

What is claimed is:

1. ln a high-voltage switching system of the type including a switching housing containing a gaseous insulating medium, and an overload arrester housing, communicative with the switching housing and containing a gaseous insulating medium having a dielectric strength the same as said medium contained in said switching system housing, a voltage overload arrester comprising only discharge current resistance means, disposed in said arrester housing, and constructed of an electrically conductive material having a zinc oxide base, for discharging current surges flowing through prises sulfur hexafluoride. 

1. In a high-voltage switching system of the type including a switching housing containing a gaseous insulating medium, and an overload arrester housing, communicative with the switching housing and containing a gaseous insulating medium having a dielectric strength the same as said medium contained in said switching system housing, a voltage overload arrester comprising only discharge current resistance means, disposed in said arrester housing, and constructed of an electrically conductive material having a zinc oxide base, for discharging current surges flowing through said switching system.
 2. The voltage overload arrester recited in claim 1, wherein said resistance means comprises a plurality of electrical resistors arranged in columnar fashion and disposed axially within said arrester housing.
 3. The voltage overload arrester recited in claim 2, wherein said switching system housing and said arrester housing are constructed of metallic material and are formed as an integral unit.
 4. The voltage overload arrester recited in claim 3, wherein said gaseous insulating medium contained in said arrester and said switching system housings comprises sulfur hexafluoride. 